The basic idea may be more than 100 years old but don't knock hard hat diving technology.
The aqualung - which has flourished since the 1950s - may have pushed it to the margins, but surface-supply helmet diving is used more than people realise.
Where submersible robots aren't suitable, professional divers still don high-tech versions of the old helmet and dress.
Modern helmet-diving is employed for specialised commercial and industrial roles, including deep saturation dives in marine oil fields.
The classic hard hat ensemble, of copper-brass helmet and canvas dress, remains popular as well.
Industrial divers right across the Third World use this kind of gear on a daily basis, while in richer countries it's sought after by historical diving groups and collectors.
Kiwi enthusiast Keith Gordon says demand from collectors has inflated the value, pricing old hard hat gear far beyond the reach of enthusiasts who'd love to restore and use it.
"It's often cheaper for us to buy new, as traditional hard hat diving gear is still mass produced in Asia, or made to order in the USA. China alone manufactures about 8,000 dive helmets annually, along with about 12,000 dresses (canvas suits)," he says.
"If you are in the market for an antique helmet, these can be found on auction web sites or at auction houses.
"With keen worldwide interest from collectors, prices can range from $5,000 to over $30,000 for a rare make of helmet. But it's a case of buyer beware!
"Many fakes made in India and Indonesia are now on the market. These are hard to tell from a real helmet and should be checked by a knowledgeable collector, or join the Historical Diving Society for advice."
Gordon says it used to be different. He tells how about 50 years a current historical diving enthusiast, Dr Harold Guy, was hitching around the South Island.
Guy was given a lift by a Timaru Harbour Board employee, who mentioned that his employer had some old hard hat gear that would soon be going to the dump.
Guy asked for, and was given, a rare 1915 Siebe Gorman dive helmet, some items of the driver's dress, plus an air pump. He restored the helmet and is still using it; a treasured piece which would now cost in the vicinity of $15,000.
Warm and dry
While Scuba equipment is generally a lot more useful, hard hat technology has a few advantages which can't be discounted.
A traditional dive helmet and dress will keep you warm and dry long after a wet-suited Scuba diver has gone hypothermic.
Hard hat divers usually have a permanent phone link to the surface and, unlike with Scuba, there's no need to keep a mouthpiece tightly clenched between the teeth.
Decompression time is required with both systems, but - unlike the swimming diver, who will eventually exhaust the gas tanks he or she carries - the hard hat diver can stay below indefinitely, depending on depth and time constraints.
Of course, hard hat diving technology has huge disadvantages as well, and more than just the obvious lack of mobility.
"The helmet and dress must be worn correctly. Getting in and out is a long, drawn-out and exacting process, requiring assistance from a couple of assistants, called 'tenders' in this game. The laborious routine is well illustrated by 1960s US Navy training videos available on YouTube.
All is forgiven
"Carrying up to 60kg of extra lead weight on your breast plate, belt and boots makes these suits excruciatingly uncomfortable on the surface. And anyone given to panic attacks is unlikely to accept a big metallic helmet being screwed and bolted down onto their head," says Gordon.
But, for most of us anyway, once under the water all is forgiven.
While sacrificing the mobility of swimming with fins, a helmet and dress provides a stable, dry, long-stay environment for a diver.
Remember, the loose-fitting diver's dress is bulky for a very good reason.
A diver inside can easily trim the amount of compressed air trapped within the suit to float up, float down, assist with the lifting of heavy weights, or "moon walk" along the bottom.
In an emergency, where the air hose is cut say, a non-return value seals his/her helmet against the water outside and the diver has a few minutes of air inside while being hauled to the surface.
"In any case, there's nothing to stop a hard hat diver carrying a small 'bail-out' air tank, for additional protection in the event of an emergency," Gordon points out.
Which way is up
Scuba divers can lose their way, forget "which way is up", or if they're inside a cave, mine shaft, or wreck - "which way is out".
Obviously hard hat divers have far less mobility to explore such places and also run the risk of snagging their air supply, but at least they'll never get lost when venturing inside them.
Their umbilical (air hose, phone line and lifeline) will always lead them back to the surface.
And they're in continual contact with a tender, who can send a second diver down to provide assistance.
There's no searching required, they just follow the lifeline, and this can also be used to haul them both to safety.
Despite the obvious handicap of trailing a lifeline everywhere, experienced hard hat divers have ventured deep inside wrecks and other confined spaces.
Gordon gives two examples of this: Surface supply divers examined almost every ship sunk in Pearl Harbour during World War II and then there's incredible story of the Bonnievale gold mine, Western Australia, which flooded in 1907.
At Bonnievale, two hard hat divers - including New Zealander Thomas Hearn - located, kept alive and eventually rescued a miner, who was trapped inside an air-pocket for nine days.
It could be that the romance of hard hat diving appeals to you and that you'd like to have a go.
But if so, it would pay to try out hard hat diving under the guidance of experienced operators, using equipment they've checked out.
These suits are a great life support systems 99 per cent of the time, and perfectly safe when used with the support required, in dive pools and at shallow-sea-depths.
They get used on public at open days (or "work days") run by classic enthusiasts and you'll be allegeable to take part, if you have a Scuba certificate.
But, as with all diving technology, there's an element of risk, perhaps best illustrated by what can happen at great depth using helmet and dress.
TV viewers following the Mythbusters series may recall the "proved verdict", after the team investigating the lurid consequences of a deep dive, in which there's both a ruptured air hose and a stuck non-return valve.
If he/she were unlucky enough to experience such failures on the same day, the result can be too awful to imagine.
If so, there's nothing to stop the great pressure deep in the ocean, of crushing a diver's body, while negative pressure caused by the severed air hose could suck flesh and soft tissues up into the pipe and much of the diver's body into the helmet.
Stories used to abound among old-time commercial divers, in which so much of a diver was sucked into his helmet that this item was later used in place of a coffin!
Okay, even at the great depths such tragedies are rare, but you can certainly see why those old-time hard hat divers checked and re-check their helmet non-return valves.
If, after pondering such matters, you're still up for a little hard hat diving, you'll need to follow the fairly nerdy Historical Diving Society Australia Pacific.
This Australasian group, which only has about 15 active members in New Zealand, is interested not only in hard hat diving, but also early double-hose scuba gear, wartime frogman equipment, early re-breathers and other unusual diving equipment. The Australian-based group keeps in close contact with its New Zealand members.
During summer, it's planned organise a "work day", which will enable Scuba-qualified members of the public to have a go at hard hat diving, both in a pool and in shallow water, at sea.
The plan is to stage such an event at Tutukaka before the end of the year.
For information on this and classic diving in general, visit: www.classicdiver.org